// Copyright 2016 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/libsampler/sampler.h"

#ifdef USE_SIGNALS

#include <errno.h>
#include <pthread.h>
#include <signal.h>
#include <sys/time.h>
#include <atomic>

#if !V8_OS_QNX && !V8_OS_AIX
#include <sys/syscall.h> // NOLINT
#endif

#if V8_OS_MACOSX
#include <mach/mach.h>
// OpenBSD doesn't have <ucontext.h>. ucontext_t lives in <signal.h>
// and is a typedef for struct sigcontext. There is no uc_mcontext.
#elif !V8_OS_OPENBSD
#include <ucontext.h>
#endif

#include <unistd.h>

#elif V8_OS_WIN || V8_OS_CYGWIN

#include "src/base/win32-headers.h"

#elif V8_OS_FUCHSIA

#include <zircon/process.h>
#include <zircon/syscalls.h>
#include <zircon/syscalls/debug.h>
#include <zircon/types.h>

// TODO(wez): Remove this once the Fuchsia SDK has rolled.
#if defined(ZX_THREAD_STATE_REGSET0)
#define ZX_THREAD_STATE_GENERAL_REGS ZX_THREAD_STATE_REGSET0
zx_status_t zx_thread_read_state(zx_handle_t h, uint32_t k, void* b, size_t l)
{
    uint32_t dummy_out_len = 0;
    return zx_thread_read_state(h, k, b, static_cast<uint32_t>(l),
        &dummy_out_len);
}
#if defined(__x86_64__)
typedef zx_x86_64_general_regs_t zx_thread_state_general_regs_t;
#else
typedef zx_arm64_general_regs_t zx_thread_state_general_regs_t;
#endif
#endif // !defined(ZX_THREAD_STATE_GENERAL_REGS)

#endif

#include <algorithm>
#include <vector>

#include "src/base/atomic-utils.h"
#include "src/base/platform/platform.h"

#if V8_OS_ANDROID && !defined(__BIONIC_HAVE_UCONTEXT_T)

// Not all versions of Android's C library provide ucontext_t.
// Detect this and provide custom but compatible definitions. Note that these
// follow the GLibc naming convention to access register values from
// mcontext_t.
//
// See http://code.google.com/p/android/issues/detail?id=34784

#if defined(__arm__)

typedef struct sigcontext mcontext_t;

typedef struct ucontext {
    uint32_t uc_flags;
    struct ucontext* uc_link;
    stack_t uc_stack;
    mcontext_t uc_mcontext;
    // Other fields are not used by V8, don't define them here.
} ucontext_t;

#elif defined(__aarch64__)

typedef struct sigcontext mcontext_t;

typedef struct ucontext {
    uint64_t uc_flags;
    struct ucontext* uc_link;
    stack_t uc_stack;
    mcontext_t uc_mcontext;
    // Other fields are not used by V8, don't define them here.
} ucontext_t;

#elif defined(__mips__)
// MIPS version of sigcontext, for Android bionic.
typedef struct {
    uint32_t regmask;
    uint32_t status;
    uint64_t pc;
    uint64_t gregs[32];
    uint64_t fpregs[32];
    uint32_t acx;
    uint32_t fpc_csr;
    uint32_t fpc_eir;
    uint32_t used_math;
    uint32_t dsp;
    uint64_t mdhi;
    uint64_t mdlo;
    uint32_t hi1;
    uint32_t lo1;
    uint32_t hi2;
    uint32_t lo2;
    uint32_t hi3;
    uint32_t lo3;
} mcontext_t;

typedef struct ucontext {
    uint32_t uc_flags;
    struct ucontext* uc_link;
    stack_t uc_stack;
    mcontext_t uc_mcontext;
    // Other fields are not used by V8, don't define them here.
} ucontext_t;

#elif defined(__i386__)
// x86 version for Android.
typedef struct {
    uint32_t gregs[19];
    void* fpregs;
    uint32_t oldmask;
    uint32_t cr2;
} mcontext_t;

typedef uint32_t kernel_sigset_t[2]; // x86 kernel uses 64-bit signal masks
typedef struct ucontext {
    uint32_t uc_flags;
    struct ucontext* uc_link;
    stack_t uc_stack;
    mcontext_t uc_mcontext;
    // Other fields are not used by V8, don't define them here.
} ucontext_t;
enum { REG_EBP = 6,
    REG_ESP = 7,
    REG_EIP = 14 };

#elif defined(__x86_64__)
// x64 version for Android.
typedef struct {
    uint64_t gregs[23];
    void* fpregs;
    uint64_t __reserved1[8];
} mcontext_t;

typedef struct ucontext {
    uint64_t uc_flags;
    struct ucontext* uc_link;
    stack_t uc_stack;
    mcontext_t uc_mcontext;
    // Other fields are not used by V8, don't define them here.
} ucontext_t;
enum { REG_RBP = 10,
    REG_RSP = 15,
    REG_RIP = 16 };
#endif

#endif // V8_OS_ANDROID && !defined(__BIONIC_HAVE_UCONTEXT_T)

namespace v8 {
namespace sampler {

#if defined(USE_SIGNALS)

    AtomicGuard::AtomicGuard(AtomicMutex* atomic, bool is_blocking)
        : atomic_(atomic)
        , is_success_(false)
    {
        do {
            bool expected = false;
            // We have to use the strong version here for the case where is_blocking
            // is false, and we will only attempt the exchange once.
            is_success_ = atomic->compare_exchange_strong(expected, true);
        } while (is_blocking && !is_success_);
    }

    AtomicGuard::~AtomicGuard()
    {
        if (!is_success_)
            return;
        atomic_->store(false);
    }

    bool AtomicGuard::is_success() const { return is_success_; }

    class Sampler::PlatformData {
    public:
        PlatformData()
            : vm_tid_(pthread_self())
        {
        }
        pthread_t vm_tid() const { return vm_tid_; }

    private:
        pthread_t vm_tid_;
    };

    void SamplerManager::AddSampler(Sampler* sampler)
    {
        AtomicGuard atomic_guard(&samplers_access_counter_);
        DCHECK(sampler->IsActive());
        pthread_t thread_id = sampler->platform_data()->vm_tid();
        auto it = sampler_map_.find(thread_id);
        if (it == sampler_map_.end()) {
            SamplerList samplers;
            samplers.push_back(sampler);
            sampler_map_.emplace(thread_id, std::move(samplers));
        } else {
            SamplerList& samplers = it->second;
            auto it = std::find(samplers.begin(), samplers.end(), sampler);
            if (it == samplers.end())
                samplers.push_back(sampler);
        }
    }

    void SamplerManager::RemoveSampler(Sampler* sampler)
    {
        AtomicGuard atomic_guard(&samplers_access_counter_);
        DCHECK(sampler->IsActive());
        pthread_t thread_id = sampler->platform_data()->vm_tid();
        auto it = sampler_map_.find(thread_id);
        DCHECK_NE(it, sampler_map_.end());
        SamplerList& samplers = it->second;
        samplers.erase(std::remove(samplers.begin(), samplers.end(), sampler),
            samplers.end());
        if (samplers.empty()) {
            sampler_map_.erase(it);
        }
    }

    void SamplerManager::DoSample(const v8::RegisterState& state)
    {
        AtomicGuard atomic_guard(&samplers_access_counter_, false);
        if (!atomic_guard.is_success())
            return;
        pthread_t thread_id = pthread_self();
        auto it = sampler_map_.find(thread_id);
        if (it == sampler_map_.end())
            return;
        SamplerList& samplers = it->second;

        for (Sampler* sampler : samplers) {
            if (!sampler->ShouldRecordSample())
                continue;
            Isolate* isolate = sampler->isolate();
            // We require a fully initialized and entered isolate.
            if (isolate == nullptr || !isolate->IsInUse())
                continue;
            if (v8::Locker::IsActive() && !Locker::IsLocked(isolate))
                continue;
            sampler->SampleStack(state);
        }
    }

    SamplerManager* SamplerManager::instance()
    {
        static base::LeakyObject<SamplerManager> instance;
        return instance.get();
    }

#elif V8_OS_WIN || V8_OS_CYGWIN

    // ----------------------------------------------------------------------------
    // Win32 profiler support. On Cygwin we use the same sampler implementation as
    // on Win32.

    class Sampler::PlatformData {
    public:
        // Get a handle to the calling thread. This is the thread that we are
        // going to profile. We need to make a copy of the handle because we are
        // going to use it in the sampler thread. Using GetThreadHandle() will
        // not work in this case. We're using OpenThread because DuplicateHandle
        // for some reason doesn't work in Chrome's sandbox.
        PlatformData()
            : profiled_thread_(OpenThread(THREAD_GET_CONTEXT | THREAD_SUSPEND_RESUME | THREAD_QUERY_INFORMATION,
                false,
                GetCurrentThreadId()))
        {
        }

        ~PlatformData()
        {
            if (profiled_thread_ != nullptr) {
                CloseHandle(profiled_thread_);
                profiled_thread_ = nullptr;
            }
        }

        HANDLE profiled_thread() { return profiled_thread_; }

    private:
        HANDLE profiled_thread_;
    };

#elif V8_OS_FUCHSIA

    class Sampler::PlatformData {
    public:
        PlatformData()
        {
            zx_handle_duplicate(zx_thread_self(), ZX_RIGHT_SAME_RIGHTS,
                &profiled_thread_);
        }
        ~PlatformData()
        {
            if (profiled_thread_ != ZX_HANDLE_INVALID) {
                zx_handle_close(profiled_thread_);
                profiled_thread_ = ZX_HANDLE_INVALID;
            }
        }

        zx_handle_t profiled_thread() { return profiled_thread_; }

    private:
        zx_handle_t profiled_thread_ = ZX_HANDLE_INVALID;
    };

#endif // USE_SIGNALS

#if defined(USE_SIGNALS)
    class SignalHandler {
    public:
        static void IncreaseSamplerCount()
        {
            base::MutexGuard lock_guard(mutex_.Pointer());
            if (++client_count_ == 1)
                Install();
        }

        static void DecreaseSamplerCount()
        {
            base::MutexGuard lock_guard(mutex_.Pointer());
            if (--client_count_ == 0)
                Restore();
        }

        static bool Installed()
        {
            base::MutexGuard lock_guard(mutex_.Pointer());
            return signal_handler_installed_;
        }

    private:
        static void Install()
        {
            struct sigaction sa;
            sa.sa_sigaction = &HandleProfilerSignal;
            sigemptyset(&sa.sa_mask);
#if V8_OS_QNX
            sa.sa_flags = SA_SIGINFO;
#else
            sa.sa_flags = SA_RESTART | SA_SIGINFO;
#endif
            signal_handler_installed_ = (sigaction(SIGPROF, &sa, &old_signal_handler_) == 0);
        }

        static void Restore()
        {
            if (signal_handler_installed_) {
                sigaction(SIGPROF, &old_signal_handler_, nullptr);
                signal_handler_installed_ = false;
            }
        }

        static void FillRegisterState(void* context, RegisterState* regs);
        static void HandleProfilerSignal(int signal, siginfo_t* info, void* context);

        // Protects the process wide state below.
        static base::LazyMutex mutex_;
        static int client_count_;
        static bool signal_handler_installed_;
        static struct sigaction old_signal_handler_;
    };

    base::LazyMutex SignalHandler::mutex_ = LAZY_MUTEX_INITIALIZER;
    int SignalHandler::client_count_ = 0;
    struct sigaction SignalHandler::old_signal_handler_;
    bool SignalHandler::signal_handler_installed_ = false;

    void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
        void* context)
    {
        USE(info);
        if (signal != SIGPROF)
            return;
        v8::RegisterState state;
        FillRegisterState(context, &state);
        SamplerManager::instance()->DoSample(state);
    }

    void SignalHandler::FillRegisterState(void* context, RegisterState* state)
    {
        // Extracting the sample from the context is extremely machine dependent.
        ucontext_t* ucontext = reinterpret_cast<ucontext_t*>(context);
#if !(V8_OS_OPENBSD || (V8_OS_LINUX && (V8_HOST_ARCH_PPC || V8_HOST_ARCH_S390)))
        mcontext_t& mcontext = ucontext->uc_mcontext;
#endif
#if V8_OS_LINUX
#if V8_HOST_ARCH_IA32
        state->pc = reinterpret_cast<void*>(mcontext.gregs[REG_EIP]);
        state->sp = reinterpret_cast<void*>(mcontext.gregs[REG_ESP]);
        state->fp = reinterpret_cast<void*>(mcontext.gregs[REG_EBP]);
#elif V8_HOST_ARCH_X64
        state->pc = reinterpret_cast<void*>(mcontext.gregs[REG_RIP]);
        state->sp = reinterpret_cast<void*>(mcontext.gregs[REG_RSP]);
        state->fp = reinterpret_cast<void*>(mcontext.gregs[REG_RBP]);
#elif V8_HOST_ARCH_ARM
#if V8_LIBC_GLIBC && !V8_GLIBC_PREREQ(2, 4)
        // Old GLibc ARM versions used a gregs[] array to access the register
        // values from mcontext_t.
        state->pc = reinterpret_cast<void*>(mcontext.gregs[R15]);
        state->sp = reinterpret_cast<void*>(mcontext.gregs[R13]);
        state->fp = reinterpret_cast<void*>(mcontext.gregs[R11]);
#else
        state->pc = reinterpret_cast<void*>(mcontext.arm_pc);
        state->sp = reinterpret_cast<void*>(mcontext.arm_sp);
        state->fp = reinterpret_cast<void*>(mcontext.arm_fp);
#endif // V8_LIBC_GLIBC && !V8_GLIBC_PREREQ(2, 4)
#elif V8_HOST_ARCH_ARM64
        state->pc = reinterpret_cast<void*>(mcontext.pc);
        state->sp = reinterpret_cast<void*>(mcontext.sp);
        // FP is an alias for x29.
        state->fp = reinterpret_cast<void*>(mcontext.regs[29]);
#elif V8_HOST_ARCH_MIPS
        state->pc = reinterpret_cast<void*>(mcontext.pc);
        state->sp = reinterpret_cast<void*>(mcontext.gregs[29]);
        state->fp = reinterpret_cast<void*>(mcontext.gregs[30]);
#elif V8_HOST_ARCH_MIPS64
        state->pc = reinterpret_cast<void*>(mcontext.pc);
        state->sp = reinterpret_cast<void*>(mcontext.gregs[29]);
        state->fp = reinterpret_cast<void*>(mcontext.gregs[30]);
#elif V8_HOST_ARCH_PPC
#if V8_LIBC_GLIBC
        state->pc = reinterpret_cast<void*>(ucontext->uc_mcontext.regs->nip);
        state->sp = reinterpret_cast<void*>(ucontext->uc_mcontext.regs->gpr[PT_R1]);
        state->fp = reinterpret_cast<void*>(ucontext->uc_mcontext.regs->gpr[PT_R31]);
#else
        // Some C libraries, notably Musl, define the regs member as a void pointer
        state->pc = reinterpret_cast<void*>(ucontext->uc_mcontext.gp_regs[32]);
        state->sp = reinterpret_cast<void*>(ucontext->uc_mcontext.gp_regs[1]);
        state->fp = reinterpret_cast<void*>(ucontext->uc_mcontext.gp_regs[31]);
#endif
#elif V8_HOST_ARCH_S390
#if V8_TARGET_ARCH_32_BIT
        // 31-bit target will have bit 0 (MSB) of the PSW set to denote addressing
        // mode.  This bit needs to be masked out to resolve actual address.
        state->pc = reinterpret_cast<void*>(ucontext->uc_mcontext.psw.addr & 0x7FFFFFFF);
#else
        state->pc = reinterpret_cast<void*>(ucontext->uc_mcontext.psw.addr);
#endif // V8_TARGET_ARCH_32_BIT
        state->sp = reinterpret_cast<void*>(ucontext->uc_mcontext.gregs[15]);
        state->fp = reinterpret_cast<void*>(ucontext->uc_mcontext.gregs[11]);
#endif // V8_HOST_ARCH_*
#elif V8_OS_IOS

#if V8_TARGET_ARCH_ARM64
        // Building for the iOS device.
        state->pc = reinterpret_cast<void*>(mcontext->__ss.__pc);
        state->sp = reinterpret_cast<void*>(mcontext->__ss.__sp);
        state->fp = reinterpret_cast<void*>(mcontext->__ss.__fp);
#elif V8_TARGET_ARCH_X64
        // Building for the iOS simulator.
        state->pc = reinterpret_cast<void*>(mcontext->__ss.__rip);
        state->sp = reinterpret_cast<void*>(mcontext->__ss.__rsp);
        state->fp = reinterpret_cast<void*>(mcontext->__ss.__rbp);
#else
#error Unexpected iOS target architecture.
#endif // V8_TARGET_ARCH_ARM64

#elif V8_OS_MACOSX
#if V8_HOST_ARCH_X64
        state->pc = reinterpret_cast<void*>(mcontext->__ss.__rip);
        state->sp = reinterpret_cast<void*>(mcontext->__ss.__rsp);
        state->fp = reinterpret_cast<void*>(mcontext->__ss.__rbp);
#elif V8_HOST_ARCH_IA32
        state->pc = reinterpret_cast<void*>(mcontext->__ss.__eip);
        state->sp = reinterpret_cast<void*>(mcontext->__ss.__esp);
        state->fp = reinterpret_cast<void*>(mcontext->__ss.__ebp);
#endif // V8_HOST_ARCH_IA32
#elif V8_OS_FREEBSD
#if V8_HOST_ARCH_IA32
        state->pc = reinterpret_cast<void*>(mcontext.mc_eip);
        state->sp = reinterpret_cast<void*>(mcontext.mc_esp);
        state->fp = reinterpret_cast<void*>(mcontext.mc_ebp);
#elif V8_HOST_ARCH_X64
        state->pc = reinterpret_cast<void*>(mcontext.mc_rip);
        state->sp = reinterpret_cast<void*>(mcontext.mc_rsp);
        state->fp = reinterpret_cast<void*>(mcontext.mc_rbp);
#elif V8_HOST_ARCH_ARM
        state->pc = reinterpret_cast<void*>(mcontext.mc_r15);
        state->sp = reinterpret_cast<void*>(mcontext.mc_r13);
        state->fp = reinterpret_cast<void*>(mcontext.mc_r11);
#endif // V8_HOST_ARCH_*
#elif V8_OS_NETBSD
#if V8_HOST_ARCH_IA32
        state->pc = reinterpret_cast<void*>(mcontext.__gregs[_REG_EIP]);
        state->sp = reinterpret_cast<void*>(mcontext.__gregs[_REG_ESP]);
        state->fp = reinterpret_cast<void*>(mcontext.__gregs[_REG_EBP]);
#elif V8_HOST_ARCH_X64
        state->pc = reinterpret_cast<void*>(mcontext.__gregs[_REG_RIP]);
        state->sp = reinterpret_cast<void*>(mcontext.__gregs[_REG_RSP]);
        state->fp = reinterpret_cast<void*>(mcontext.__gregs[_REG_RBP]);
#endif // V8_HOST_ARCH_*
#elif V8_OS_OPENBSD
#if V8_HOST_ARCH_IA32
        state->pc = reinterpret_cast<void*>(ucontext->sc_eip);
        state->sp = reinterpret_cast<void*>(ucontext->sc_esp);
        state->fp = reinterpret_cast<void*>(ucontext->sc_ebp);
#elif V8_HOST_ARCH_X64
        state->pc = reinterpret_cast<void*>(ucontext->sc_rip);
        state->sp = reinterpret_cast<void*>(ucontext->sc_rsp);
        state->fp = reinterpret_cast<void*>(ucontext->sc_rbp);
#endif // V8_HOST_ARCH_*
#elif V8_OS_SOLARIS
        state->pc = reinterpret_cast<void*>(mcontext.gregs[REG_PC]);
        state->sp = reinterpret_cast<void*>(mcontext.gregs[REG_SP]);
        state->fp = reinterpret_cast<void*>(mcontext.gregs[REG_FP]);
#elif V8_OS_QNX
#if V8_HOST_ARCH_IA32
        state->pc = reinterpret_cast<void*>(mcontext.cpu.eip);
        state->sp = reinterpret_cast<void*>(mcontext.cpu.esp);
        state->fp = reinterpret_cast<void*>(mcontext.cpu.ebp);
#elif V8_HOST_ARCH_ARM
        state->pc = reinterpret_cast<void*>(mcontext.cpu.gpr[ARM_REG_PC]);
        state->sp = reinterpret_cast<void*>(mcontext.cpu.gpr[ARM_REG_SP]);
        state->fp = reinterpret_cast<void*>(mcontext.cpu.gpr[ARM_REG_FP]);
#endif // V8_HOST_ARCH_*
#elif V8_OS_AIX
        state->pc = reinterpret_cast<void*>(mcontext.jmp_context.iar);
        state->sp = reinterpret_cast<void*>(mcontext.jmp_context.gpr[1]);
        state->fp = reinterpret_cast<void*>(mcontext.jmp_context.gpr[31]);
#endif // V8_OS_AIX
    }

#endif // USE_SIGNALS

    Sampler::Sampler(Isolate* isolate)
        : isolate_(isolate)
        , data_(base::make_unique<PlatformData>())
    {
    }

    Sampler::~Sampler()
    {
        DCHECK(!IsActive());
    }

    void Sampler::Start()
    {
        DCHECK(!IsActive());
        SetActive(true);
#if defined(USE_SIGNALS)
        SignalHandler::IncreaseSamplerCount();
        SamplerManager::instance()->AddSampler(this);
#endif
    }

    void Sampler::Stop()
    {
#if defined(USE_SIGNALS)
        SamplerManager::instance()->RemoveSampler(this);
        SignalHandler::DecreaseSamplerCount();
#endif
        DCHECK(IsActive());
        SetActive(false);
    }

#if defined(USE_SIGNALS)

    void Sampler::DoSample()
    {
        if (!SignalHandler::Installed())
            return;
        DCHECK(IsActive());
        SetShouldRecordSample();
        pthread_kill(platform_data()->vm_tid(), SIGPROF);
    }

#elif V8_OS_WIN || V8_OS_CYGWIN

    void Sampler::DoSample()
    {
        HANDLE profiled_thread = platform_data()->profiled_thread();
        if (profiled_thread == nullptr)
            return;

        const DWORD kSuspendFailed = static_cast<DWORD>(-1);
        if (SuspendThread(profiled_thread) == kSuspendFailed)
            return;

        // Context used for sampling the register state of the profiled thread.
        CONTEXT context;
        memset(&context, 0, sizeof(context));
        context.ContextFlags = CONTEXT_FULL;
        if (GetThreadContext(profiled_thread, &context) != 0) {
            v8::RegisterState state;
#if V8_HOST_ARCH_X64
            state.pc = reinterpret_cast<void*>(context.Rip);
            state.sp = reinterpret_cast<void*>(context.Rsp);
            state.fp = reinterpret_cast<void*>(context.Rbp);
#elif V8_HOST_ARCH_ARM64
            state.pc = reinterpret_cast<void*>(context.Pc);
            state.sp = reinterpret_cast<void*>(context.Sp);
            state.fp = reinterpret_cast<void*>(context.Fp);
#else
            state.pc = reinterpret_cast<void*>(context.Eip);
            state.sp = reinterpret_cast<void*>(context.Esp);
            state.fp = reinterpret_cast<void*>(context.Ebp);
#endif
            SampleStack(state);
        }
        ResumeThread(profiled_thread);
    }

#elif V8_OS_FUCHSIA

    void Sampler::DoSample()
    {
        zx_handle_t profiled_thread = platform_data()->profiled_thread();
        if (profiled_thread == ZX_HANDLE_INVALID)
            return;

        zx_handle_t suspend_token = ZX_HANDLE_INVALID;
        if (zx_task_suspend_token(profiled_thread, &suspend_token) != ZX_OK)
            return;

        // Wait for the target thread to become suspended, or to exit.
        // TODO(wez): There is currently no suspension count for threads, so there
        // is a risk that some other caller resumes the thread in-between our suspend
        // and wait calls, causing us to miss the SUSPENDED signal. We apply a 100ms
        // deadline to protect against hanging the sampler thread in this case.
        zx_signals_t signals = 0;
        zx_status_t suspended = zx_object_wait_one(
            profiled_thread, ZX_THREAD_SUSPENDED | ZX_THREAD_TERMINATED,
            zx_deadline_after(ZX_MSEC(100)), &signals);
        if (suspended != ZX_OK || (signals & ZX_THREAD_SUSPENDED) == 0) {
            zx_handle_close(suspend_token);
            return;
        }

        // Fetch a copy of its "general register" states.
        zx_thread_state_general_regs_t thread_state = {};
        if (zx_thread_read_state(profiled_thread, ZX_THREAD_STATE_GENERAL_REGS,
                &thread_state, sizeof(thread_state))
            == ZX_OK) {
            v8::RegisterState state;
#if V8_HOST_ARCH_X64
            state.pc = reinterpret_cast<void*>(thread_state.rip);
            state.sp = reinterpret_cast<void*>(thread_state.rsp);
            state.fp = reinterpret_cast<void*>(thread_state.rbp);
#elif V8_HOST_ARCH_ARM64
            state.pc = reinterpret_cast<void*>(thread_state.pc);
            state.sp = reinterpret_cast<void*>(thread_state.sp);
            state.fp = reinterpret_cast<void*>(thread_state.r[29]);
#endif
            SampleStack(state);
        }

        zx_handle_close(suspend_token);
    }

// TODO(wez): Remove this once the Fuchsia SDK has rolled.
#if defined(ZX_THREAD_STATE_REGSET0)
#undef ZX_THREAD_STATE_GENERAL_REGS
#endif

#endif // USE_SIGNALS

} // namespace sampler
} // namespace v8
